Jacques Chirac led a French walkout from the opening session of the EU's annual spring summit last night when a fellow Frenchman committed the grave offence of speaking English.

Highlighting France's acute sensitivity towards the decline of the language which once dominated the EU, Mr Chirac led three senior ministers out of the talks when Ernest-Antoine Seillière, the French head of the European employers' group Unice, abandoned his mother tongue on the ground that English is "the language of business".

Mr Chirac picked up his papers and left, with Philippe Douste-Blazy, the foreign minister and Thierry Breton, the finance minister, in tow. Gallic pride was soon restored when Jean-Claude Trichet, the French head of the European Central Bank, addressed the meeting in his mother tongue - and Mr Chirac led his ministers back.

The walkout set the scene for what is expected to be an inconclusive summit ending at lunchtime today.

France and Germany are at loggerheads over the economic future of Europe after Angela Merkel criticised French attempts to limit foreign investment. In the most serious Franco-German disagreement since her election as chancellor in November, Ms Merkel dismissed a French initiative to promote "economic patriotism". "We can only have an internal market when electricity flows freely and when we accept European champions and not just think nationally," the German chancellor said as she arrived at the summit in Brussels yesterday.

Ms Merkel, who has made clear that she wants to open up the Franco-German alliance after the closed years of Mr Chirac and Gerhard Schröder, was aiming at the French on two fronts. Dominique de Villepin, the French prime minister, has pledged to champion "economic patriotism" by naming 11 French business sectors which should be shielded from foreign bidders. France is also facing accusations of protectionism by blocking a takeover of Suez, the Franco-Belgian energy giant, by its Italian rival, Enel.

Austria, chairing the summit as part of its six-month EU presidency, had hoped to reach out to disillusioned voters by focusing on bread-and-butter issues. A successful summit would reinvigorate the so-called "Lisbon agenda" on economic reform and pave the way for a discussion on how to reform the EU after a rejection of the European constitution last year.

But a rise in protectionism in Europe and resistance to reforms, which has prompted the worst riots in the centre of Paris for a decade, have cast a cloud over the gathering. Jean-Claude Juncker, the Luxembourg prime minister, defended his attempts to resist a takeover of the Luxembourg-based steelmaker Arcelor by Mittal Steel. "Sometimes governments have good arguments," he said.

The Italian government made its exasperation clear. Pier Ferdinando Casini, the speaker of the Italian parliament, mocked any government that restricted cross-border takeovers.

"Either you are a pretend European, and therefore in favour of protectionism and nationalism, or else you are a real European and want to stimulate competition," he told reporters at a pre-summit meeting of conservative leaders.